The insulin-like growth factor-I/binding protein axis: physiology, pathophysiology and therapeutic manipulation.

Insulin-like growth factor-I (IGF-I) is a single-chain polypeptide which has multiple metabolic actions and effects on the differentiation and proliferation of a wide variety of cell types. IGF-I has endocrine, paracrine and autocrine actions and is bound in the circulation to a complex system of binding proteins which alter its bioavailability and activity. Thus its physiology is complex and is altered in a number of pathological states. This review will discuss these states and the actual and proposed therapeutic applications of recombinant human IGF-I (rhIGF-I).